To suppress electro magnetic interference (EMI) caused by semiconductor devices, electromagnetic shields may be formed on the surfaces of semiconductor packages. On the occasion of forming electromagnetic shields on semiconductor packages, the semiconductor packages are mounted on a conveyance carrier such that the rear surfaces (substrate-side surfaces) of the semiconductor packages face the conveyance carrier. When electromagnetic shield material is formed on the surfaces of the semiconductor packages, the electromagnetic shield material is also formed on the surface of the conveyance carrier between every neighboring two of the plurality of semiconductor packages. That is, the electromagnetic shield material is formed as a continuous film on the surfaces of the semiconductor packages and the surface of the conveyance carrier. In this case, after the electromagnetic shields are formed, when the semiconductor packages are detached from the conveyance carrier, electromagnetic shield material burrs form on the outer edges of the semiconductor packages.